Hydraulic system



R. E. PRICE HYDRAULIC SYSTEM Filed Nov. 1945 RALPH E. PRICE llwcntor Patented May 30, 1950 HYDRAULIC SYSTEM Ralph E. Price, Highfield, Md., assignor to Landis Tool Company, Waynesboro, Pa.

Application November 1, 1946, Serial No. 707,281

This invention relates to hydraulic systems wherein use is made of very small volumes of fluid under pressure.

A limitation in any type of hydraulic pump is the ratio between volume of discharge and leakage. Where the capacity of the pump is large, the leakage is relatively small. In very small pumps the leakage may be equal to the discharge volume. Leakage is due to the fact that it is practically impossible to fit the running parts of a pump so that it will discharge a volume equal to its displacement. Clearances necessary to permit relative movement of parts also permit loss of fluid. A small amount of leakage occurs through relief valves and other types of valves. As mentioned above, this is more pronounced where the volume is small, since for a given system and pressure the leakage probably remains constant regardless of the volume passing through.

It is therefore an object of this invention to provide means for reducing leakage of fluid under pressure in a low capacit hydraulic system.

A further object is to provide two sources of fluid under pressure in which the pressure in one system regulates the pressure in the other system.

A further object is to provide a hydraulic system including differential pumps and means for reducing leakage in the differential output.

The drawing is a plan view of a grinding machine showing a grindin wheel feed mechanism which makes use of the hydraulic system which is the subject of this invention.

In the drawing, numeral ll] indicates the bed of a grinding machine, H a grinding wheel support slidably mounted thereon, and I2 a grinding wheel rotatably mounted on said support. A work carriage I3 is slidably mounted on bed In for movement in a direction transverse to that of the wheel support. Said work carriage has a headstock I4 and a footstock l5 mounted thereon for rotatably supporting a work piece to be operated on by said grinding wheel.

The means for effecting movement of wheel base II is described in detail in Patent No. 2,313,479, granted March 9, 1943.

This means consists of a piston 20 slidable in a cylinder 2| in bed m. Said piston has a piston rod 23 in the form of a feed screw. The threads of said screw are in operative engagement with the teeth of a worm wheel 24. positive stop 26 limits the endwise movement of feedscrew 23. Said worm wheel 24 is on the lower end of a vertical shaft 25 passing through 7 Claims. (Cl. 60-52) means of a handwheel 21 to which it is connected by suitable gearing.

The means for effecting a grinding feed movement of wheel base consists of a piston 30 slidably mounted in a cylinder 3| in bed l0. Said piston has a rod 32 on which rack teeth have been formed for engaging the teeth of gear 33 on piston rod 23 of piston 2|]. The length of stroke of piston 30 may be regulated by adjusting screw 34.

Fluid under pressure for actuating piston 23 in both directions and for resetting piston 30 is supplied by a pump 40 having an inlet 4| and a discharge line 42. A relief valve 43 is connected to said line 42. Line 42 leads to a reversing valve 44 from which fluid under pressure may be directed alternately through lines 45 and 46. Exhaust fluid from said lines is discharged through ports 41 and 48.

Fluid under pressure for moving piston 30 from right to left for the feeding movement is supplied by a pair of pumps 5|] and 5| of the same displacement, However, pump is operated at a slightly higher speed than pump 5| and therefore its output is proportionately higher. Pump 50 has an inlet 52 and a discharge line 53 leading to the right hand end of cylinder 3|. Pump 5| is connected to line 53 and pumps from said line to the extents of its capacity. Pump 5| discharges through line 54, check valve and line 56 to line 53. A by pass valve 51 is connected to line 54 so that the output of pump. 5i may be returned to a reservoir (not shown). The function of check valve 55 is to prevent the output of pump 50 from flowing through lines 56, 54 and out through valve 5'! when said valve is open.

There is no relief valve in this two pump system. The reason for this is because of the small volume of fluid passing through the system and the fact that conventional relief valves usually leak enough to interfere with the operation of such a low volume system.

Instead of using a conventional relief valve, a check valve is inserted in line 6| connecting line 56 of the two pump system with line 46 of the rapid feed pressure system. This rapid feed system operates at a higher pressure than is required to move piston 30 and thus serves to hold valve 6|] in closed position except when for any reason, the pressure in the two pump system becomes greater than that in the rapid feed system as when piston 30 stops at the end of its movement, in which case said valve will the wheel base ll. Said shaft may be rotated by 55 relieve the higher pressure into the rapid feed 53, 56, valve fiiland line 6| through line, 45 and.

reversing valve 44-"to exhaust line 48':

Operation The feeding movement of grinding wheel I!" may be initiated by shifting valve 44 to therightagainst spring 62. In this position fluid under pressure from pump 40 will 'be-directed'through' line 46 to cylinder 2| causing pistonZilto drive" wheel base II to forward or operative position against stop 26. Pressure will be maintained in line 46 to hold screw 23 against said stop until the end of the grinding cycle when reversing valve-=44 will be shifted to reset the feed mecha nism. Also in this position switch 64' will be closed to initiate operationof timer 63"which will energizesolenoid65*tohold said switch closed; At thesame time, pumps 50 and-| supply-fluid underpressure through lines 53; 54 and'56-to the Piston 36 andright hand' end of cylinder 3 I. piston rod 32- rotate screw 23 so that at the end of the rapid feed movement'of piston 26 determined bystop 26, the wheel support II will continue to move at a rate suitable-for grinding due to the rotation of screw 23in contact with worm wheel 24: except by handwheel 2 i, it acts as a nut and moves alongscrew 23"carrying wheel base I i with it;

After a predetermined amount of grinding which may, be determined by either a sizing deviceor the timing" mechanism 63, valve 5 1 ac tuated by said timer is opened'and theoutput of pump 5| is returned to thereservoirlnot shown).

Since'pump 5| is suppliedby pump 56 which has a" slightly higher output, the small volume which is the difference between the discharge volumeof thetwo pumps continues to fiow through line- 53 to cylinder 3| The movement if piston 36 and'hence the rate of grinding feed isthus reduced in-proportion to the reduction in volumeof fluid-supplied thereto. When this movement is .timer controlled as it is in this case, piston may' reach'the end'of itsstroke before the. end of the timed period.

The pressure in line 53; therefore, will build upmatically, to the .left'hand position: In this case timer 63 breaksthe circuit'to' solenoid |i5--permitting spring 62 to shift valve-'44 to the-left and at the same time open switch 64; In this position of Vai /e441, line 46-wi'll be opened to 'exhaust port- 48. Fluid under" pressure will. be directed through line 45 tocylinders 21 and 3| toireset. feed pistons 20 and 3|] respectively. Exhaustxfluidx from cylindert Iwill pass through line 53 against pressure from pump 50:01- both of, the pumps-5m and 51 and through line156 and valvet!) to;1ine- 46 which is connected to exhaust linesfiethrough reversing valve 44. In therabsence, of. pressure in line 46 checkvalve Ell-will open due to thepres:

sure-behind it and connectthe-twopump system.

including line 53 and cylinder. 3| to-exhaust.

Fluid under pressure from pump 40 will de Since said" worm wheel cannot be rotated At thispoint, check'valve 60= directed through line 45 which divides to supply fluid to the rod ends of both of the cylinders 2| and 3| thus retracting wheel l2 and resetting the grinding feed piston 3|] against screw 34.

I claim:

1. A hydraulic system having a low volume section and a high volume section, said high volumesection. including, a motor,,a pump for supplying fluid under pressure thereto and a relief valve for relieving excess fluid, said low volume section including a motor and a source of fluid under pressure, a check valve between said low volume section and said high volume section,

saidcheck valve acting as a relief valve, the setting of which is dependent on the pressure in the high volume section and arranged to prevent a flow of" fluid from..said high volume section to said low volume section.

2. A hydraulic system having a low volume section and a high volume section, said high volume section including a motor, a pump for supplying fiuid'under pressure thereto and a relief valve for relieving excess fluid, said low volume section including a motor and a source of fiuid under pressure, a connection between said high volume section and said low volume section,,

acheck. valve in said connection arranged to permit escape of excess fluid from said low volume section to said, high volume section when the pressure in said low volume section is greater than the pressure in said high volume section.

3,.A., hydraulic system having a low volume section and. a high volume section, said high volume. section including a motor, a pump for supplying fluiduncier pressure thereto and a relief valve for relieving excess fluid, said low volume, section including a motor and a source of. fluid under pressure, a connection between said high volume section and said low volume section, a check valve in said connection arranged to permit relief into said high volume section of pressure in said low volume section in excess of, the pressure in said high volume section.

4. A hydraulic system having a low volume section anda high volume section, said high volume section including amotor, a pump, for supplying fluid under pressure thereto and a relief valve for relieving, excess. fluid, said low volume section including a motor. and a source of fiuid. under pressure, a connection between.

said high volume section and'said low volume section, a check valve in said connection, said check valve being held in closed position by the. fluid,in'saidhigh-volume section, said fluid and said check valve combining to regulate the pressure in said low volume section.

5. In ahydraulic system, a hydraulic motor, a.

.. source of. fluid under pressure for said motor from the larger pump to saidmotor for conduct! ing the small volume of "fluid which is the differencein capacitiesof the two pumps, a by pass valve for'diverting the output of the smaller, pump, acheck' valve between-the motor and said.- valve, a second hydraulic systemtoperable at a.

higher. pressure than said first system, a. COD-r nection includinga check valve between said first system. and. said second system whereby an excess, of pressure insaid' first system will be re- .leased'into said'second system at a pressuredetermined, by the pressure insaid secondsystem;

d. In a hydraulic system having a motor, a high volume and a low volume section, the method of preventing leakage in said low volume section which consists in connecting said sections, placing a check valve in said connection positioned to permit passage of fluid from said low volume section to said high volume section, using the high pressure in said high volume section to hold said valve closed during movement of said motor but permitting the relief of excess pressure in said low volume section into said high volume section when the pressure in said low volume section is greater than the pressure in said high volume section.

7. A hydraulic system having a low volume section and a high volume section, the high volume section including a motor, a pump for supplying the fluid under pressure thereto, and a relief valve for relieving excess fluid in said system, said low volume section including a motor and a source of fluid under pressure acting coristantly on said motor in one direction, a reversing valve for directing fluid from said first pump alternately to opposite sides of said first motor and to one side of said second motor, a check valve between said low volume section and said high volume section for discharging fluid from said low volume section into said high volume section when said low volume motor is moved in opposition to said low volume fluid supply.

RALPH E. PRICE.

REFERENCES CITED UNITED STATES PATENTS Name Date Tucker May 4, 1943 Number 

